In the hinge field it is often necessary to control the angular position of a first member which is rotatably coupled to a second member by the hinge. A common application of such a hinge would be in laptop, notebook, and palmtop computers to allow a user to position the liquid crystal display screen. In a notebook computer, for example, the hinge housing is normally structurally fastened to the base of the computer and the shaft is connected to the screen of the computer. When the screen is rotated, it is held in any angular position by the torque generated between the friction elements in the hinge and the shaft.
Referring to FIGS. 1 and 2, there is shown a prior art hinge assembly, generally designated 10, for rotatably coupling a first member (not shown) to a second member (not shown). An example of the first and second members includes the base and screen, respectively, of the notebook computer mentioned above. However, the first and second members can be any members wherein it is desired to control the angular position of one member with respect to the other.
The hinge assembly 10 includes a friction element 12 for being secured to the first member. The friction element 12 is generally in the form of a question mark in cross section. That is, the friction element 12 includes a barrel or knuckle portion 12a and a leg or leaf 12b extending therefrom for being connected to the first member. The barrel 12a of the friction element includes an internal surface 14 which defines a generally cylindrical cavity 16.
The hinge assembly further includes a generally cylindrical pintle 18 for being secured to the second member. The pintle 18 includes an external surface 20. The pintle 18 is positioned within the cavity 16 with the external surface 20 of the pintle 18 in frictional engagement with a portion of the internal surface 14 of the friction element 12 such that torque is created between the friction element 12 and the pintle 18 for allowing the friction element 12 to be held in an infinitely variable angular position with respect to the pintle 18.
The prior art hinge assembly shown in FIGS. 1 and 2 is characterized by a relatively short performance life. The hinge assembly 10 suffers significant design limitations since the internal surface 14 of the friction element 12 only contacts the pintle 18 in three small sectors along the external surface 20 of the pintle 18. Because all of the forces transferred between the friction element 12 and pintle 18 are highly localized (as depicted by force vectors 22), there is significant pressure created at the contact areas which causes the hinge assembly to fatigue and have a loss of torque after a relatively short period of time. That is, the ability to control the angular position of the friction element 12 with respect to the pintle 18 is quickly reduced to the point where the relative angular positions cannot be controlled.
The highly localized forces are created because the outside diameter of the pintle 18 is greater than or equal to the inside diameter of the cavity 16 of the friction element 12 to create an interference fit between the friction element 12 and pintle 18. When the pintle 18 is inserted within the cavity 16, the friction element 12 bends in a non-uniform manner to accommodate the pintle 18. As a result of the non-uniform bending, gaps 24 are created between the internal surface 14 of the friction element 12 and the external surface 20 of the pintle 18. Further, the bending also results in highly localized forces applied across the top of the friction element 12 and slightly smaller forces being applied on opposite sides of the pintle 18 along the lower edge of the friction element 12. The direction and location of the forces are depicted by the force vectors 22a, 22b shown in FIG. 2. The length of the force vectors 22a, 22b are depicted in accordance with the magnitude of the forces actually applied between the friction element 12 and the pintle 18.
Furthermore, the hinge assembly 10 shown in FIGS. 1 and 2 does not include any means for retaining lubricant between the friction element 12 and the pintle 18 during operation. In general, lubricant is gradually forced out from between the internal surface 14 of the friction element 12 and the external surface 20 of the pintle 18 by the regular, repeated, clockwise and counterclockwise motions of the hinge assembly 10. This contributes to the relatively short hinge life and to noise being generated in the hinge assembly 10 after a sufficient amount of lubricant has been forced out from between the friction element 12 and pintle 18.
The present invention overcomes many of the disadvantages inherent in the conventional hinge assembly 10 by providing a friction element which creates uniform forces between the external surface of the pintle and the internal surface of the friction element, thereby lowering the local pressures between the friction element and the pintle, increasing the operating life of the hinge assembly as well as providing for more efficient torque transfer, and ultimately, smaller size than prior art hinge assemblies. The hinge assembly of the present invention further includes areas for retaining lubrication between the pintle 18 and friction element 12 to further increase the operating life of the hinge assembly. This improvement also contributes to the relatively long operating life of the invention, as compared to prior art hinge assemblies.